mfd: Add ChromeOS EC SPI driver

This uses a SPI bus to talk to the ChromeOS EC. The protocol
is defined by the EC and is fairly simple, with a length byte,
checksum, command byte and version byte (to permit easy creation
of new commands).

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

drivers/mfd/Kconfig

@@ -39,6 +39,16 @@ config MFD_CROS_EC_I2C
 	  a checksum. Failing accesses will be retried three times to
 	  improve reliability.
 
+config MFD_CROS_EC_SPI
+	tristate "ChromeOS Embedded Controller (SPI)"
+	depends on MFD_CROS_EC && SPI
+
+	---help---
+	  If you say Y here, you get support for talking to the ChromeOS EC
+	  through a SPI bus, using a byte-level protocol. Since the EC's
+	  response time cannot be guaranteed, we support ignoring
+	  'pre-amble' bytes before the response actually starts.
+
 config MFD_88PM800
 	tristate "Support Marvell 88PM800"
 	depends on I2C=y && GENERIC_HARDIRQS

drivers/mfd/Makefile

@@ -10,6 +10,7 @@ obj-$(CONFIG_MFD_SM501)		+= sm501.o
 obj-$(CONFIG_MFD_ASIC3)		+= asic3.o tmio_core.o
 obj-$(CONFIG_MFD_CROS_EC)	+= cros_ec.o
 obj-$(CONFIG_MFD_CROS_EC_I2C)	+= cros_ec_i2c.o
+obj-$(CONFIG_MFD_CROS_EC_SPI)	+= cros_ec_spi.o
 
 rtsx_pci-objs			:= rtsx_pcr.o rts5209.o rts5229.o rtl8411.o rts5227.o
 obj-$(CONFIG_MFD_RTSX_PCI)	+= rtsx_pci.o

drivers/mfd/cros_ec_spi.c

@@ -0,0 +1,375 @@
+/*
+ * ChromeOS EC multi-function device (SPI)
+ *
+ * Copyright (C) 2012 Google, Inc
+ *
+ * This software is licensed under the terms of the GNU General Public
+ * License version 2, as published by the Free Software Foundation, and
+ * may be copied, distributed, and modified under those terms.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/delay.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/mfd/cros_ec.h>
+#include <linux/mfd/cros_ec_commands.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/spi/spi.h>
+
+
+/* The header byte, which follows the preamble */
+#define EC_MSG_HEADER			0xec
+
+/*
+ * Number of EC preamble bytes we read at a time. Since it takes
+ * about 400-500us for the EC to respond there is not a lot of
+ * point in tuning this. If the EC could respond faster then
+ * we could increase this so that might expect the preamble and
+ * message to occur in a single transaction. However, the maximum
+ * SPI transfer size is 256 bytes, so at 5MHz we need a response
+ * time of perhaps <320us (200 bytes / 1600 bits).
+ */
+#define EC_MSG_PREAMBLE_COUNT		32
+
+/*
+  * We must get a response from the EC in 5ms. This is a very long
+  * time, but the flash write command can take 2-3ms. The EC command
+  * processing is currently not very fast (about 500us). We could
+  * look at speeding this up and making the flash write command a
+  * 'slow' command, requiring a GET_STATUS wait loop, like flash
+  * erase.
+  */
+#define EC_MSG_DEADLINE_MS		5
+
+/*
+  * Time between raising the SPI chip select (for the end of a
+  * transaction) and dropping it again (for the next transaction).
+  * If we go too fast, the EC will miss the transaction. It seems
+  * that 50us is enough with the 16MHz STM32 EC.
+  */
+#define EC_SPI_RECOVERY_TIME_NS	(50 * 1000)
+
+/**
+ * struct cros_ec_spi - information about a SPI-connected EC
+ *
+ * @spi: SPI device we are connected to
+ * @last_transfer_ns: time that we last finished a transfer, or 0 if there
+ *	if no record
+ */
+struct cros_ec_spi {
+	struct spi_device *spi;
+	s64 last_transfer_ns;
+};
+
+static void debug_packet(struct device *dev, const char *name, u8 *ptr,
+			  int len)
+{
+#ifdef DEBUG
+	int i;
+
+	dev_dbg(dev, "%s: ", name);
+	for (i = 0; i < len; i++)
+		dev_cont(dev, " %02x", ptr[i]);
+#endif
+}
+
+/**
+ * cros_ec_spi_receive_response - Receive a response from the EC.
+ *
+ * This function has two phases: reading the preamble bytes (since if we read
+ * data from the EC before it is ready to send, we just get preamble) and
+ * reading the actual message.
+ *
+ * The received data is placed into ec_dev->din.
+ *
+ * @ec_dev: ChromeOS EC device
+ * @need_len: Number of message bytes we need to read
+ */
+static int cros_ec_spi_receive_response(struct cros_ec_device *ec_dev,
+					int need_len)
+{
+	struct cros_ec_spi *ec_spi = ec_dev->priv;
+	struct spi_transfer trans;
+	struct spi_message msg;
+	u8 *ptr, *end;
+	int ret;
+	unsigned long deadline;
+	int todo;
+
+	/* Receive data until we see the header byte */
+	deadline = jiffies + msecs_to_jiffies(EC_MSG_DEADLINE_MS);
+	do {
+		memset(&trans, '\0', sizeof(trans));
+		trans.cs_change = 1;
+		trans.rx_buf = ptr = ec_dev->din;
+		trans.len = EC_MSG_PREAMBLE_COUNT;
+
+		spi_message_init(&msg);
+		spi_message_add_tail(&trans, &msg);
+		ret = spi_sync(ec_spi->spi, &msg);
+		if (ret < 0) {
+			dev_err(ec_dev->dev, "spi transfer failed: %d\n", ret);
+			return ret;
+		}
+
+		for (end = ptr + EC_MSG_PREAMBLE_COUNT; ptr != end; ptr++) {
+			if (*ptr == EC_MSG_HEADER) {
+				dev_dbg(ec_dev->dev, "msg found at %d\n",
+					ptr - ec_dev->din);
+				break;
+			}
+		}
+
+		if (time_after(jiffies, deadline)) {
+			dev_warn(ec_dev->dev, "EC failed to respond in time\n");
+			return -ETIMEDOUT;
+		}
+	} while (ptr == end);
+
+	/*
+	 * ptr now points to the header byte. Copy any valid data to the
+	 * start of our buffer
+	 */
+	todo = end - ++ptr;
+	BUG_ON(todo < 0 || todo > ec_dev->din_size);
+	todo = min(todo, need_len);
+	memmove(ec_dev->din, ptr, todo);
+	ptr = ec_dev->din + todo;
+	dev_dbg(ec_dev->dev, "need %d, got %d bytes from preamble\n",
+		 need_len, todo);
+	need_len -= todo;
+
+	/* Receive data until we have it all */
+	while (need_len > 0) {
+		/*
+		 * We can't support transfers larger than the SPI FIFO size
+		 * unless we have DMA. We don't have DMA on the ISP SPI ports
+		 * for Exynos. We need a way of asking SPI driver for
+		 * maximum-supported transfer size.
+		 */
+		todo = min(need_len, 256);
+		dev_dbg(ec_dev->dev, "loop, todo=%d, need_len=%d, ptr=%d\n",
+			todo, need_len, ptr - ec_dev->din);
+
+		memset(&trans, '\0', sizeof(trans));
+		trans.cs_change = 1;
+		trans.rx_buf = ptr;
+		trans.len = todo;
+		spi_message_init(&msg);
+		spi_message_add_tail(&trans, &msg);
+
+		/* send command to EC and read answer */
+		BUG_ON((u8 *)trans.rx_buf - ec_dev->din + todo >
+				ec_dev->din_size);
+		ret = spi_sync(ec_spi->spi, &msg);
+		if (ret < 0) {
+			dev_err(ec_dev->dev, "spi transfer failed: %d\n", ret);
+			return ret;
+		}
+
+		debug_packet(ec_dev->dev, "interim", ptr, todo);
+		ptr += todo;
+		need_len -= todo;
+	}
+
+	dev_dbg(ec_dev->dev, "loop done, ptr=%d\n", ptr - ec_dev->din);
+
+	return 0;
+}
+
+/**
+ * cros_ec_command_spi_xfer - Transfer a message over SPI and receive the reply
+ *
+ * @ec_dev: ChromeOS EC device
+ * @ec_msg: Message to transfer
+ */
+static int cros_ec_command_spi_xfer(struct cros_ec_device *ec_dev,
+				    struct cros_ec_msg *ec_msg)
+{
+	struct cros_ec_spi *ec_spi = ec_dev->priv;
+	struct spi_transfer trans;
+	struct spi_message msg;
+	int i, len;
+	u8 *ptr;
+	int sum;
+	int ret = 0, final_ret;
+	struct timespec ts;
+
+	len = cros_ec_prepare_tx(ec_dev, ec_msg);
+	dev_dbg(ec_dev->dev, "prepared, len=%d\n", len);
+
+	/* If it's too soon to do another transaction, wait */
+	if (ec_spi->last_transfer_ns) {
+		struct timespec ts;
+		unsigned long delay;	/* The delay completed so far */
+
+		ktime_get_ts(&ts);
+		delay = timespec_to_ns(&ts) - ec_spi->last_transfer_ns;
+		if (delay < EC_SPI_RECOVERY_TIME_NS)
+			ndelay(delay);
+	}
+
+	/* Transmit phase - send our message */
+	debug_packet(ec_dev->dev, "out", ec_dev->dout, len);
+	memset(&trans, '\0', sizeof(trans));
+	trans.tx_buf = ec_dev->dout;
+	trans.len = len;
+	trans.cs_change = 1;
+	spi_message_init(&msg);
+	spi_message_add_tail(&trans, &msg);
+	ret = spi_sync(ec_spi->spi, &msg);
+
+	/* Get the response */
+	if (!ret) {
+		ret = cros_ec_spi_receive_response(ec_dev,
+				ec_msg->in_len + EC_MSG_TX_PROTO_BYTES);
+	} else {
+		dev_err(ec_dev->dev, "spi transfer failed: %d\n", ret);
+	}
+
+	/* turn off CS */
+	spi_message_init(&msg);
+	final_ret = spi_sync(ec_spi->spi, &msg);
+	ktime_get_ts(&ts);
+	ec_spi->last_transfer_ns = timespec_to_ns(&ts);
+	if (!ret)
+		ret = final_ret;
+	if (ret < 0) {
+		dev_err(ec_dev->dev, "spi transfer failed: %d\n", ret);
+		return ret;
+	}
+
+	/* check response error code */
+	ptr = ec_dev->din;
+	if (ptr[0]) {
+		dev_warn(ec_dev->dev, "command 0x%02x returned an error %d\n",
+			 ec_msg->cmd, ptr[0]);
+		debug_packet(ec_dev->dev, "in_err", ptr, len);
+		return -EINVAL;
+	}
+	len = ptr[1];
+	sum = ptr[0] + ptr[1];
+	if (len > ec_msg->in_len) {
+		dev_err(ec_dev->dev, "packet too long (%d bytes, expected %d)",
+			len, ec_msg->in_len);
+		return -ENOSPC;
+	}
+
+	/* copy response packet payload and compute checksum */
+	for (i = 0; i < len; i++) {
+		sum += ptr[i + 2];
+		if (ec_msg->in_len)
+			ec_msg->in_buf[i] = ptr[i + 2];
+	}
+	sum &= 0xff;
+
+	debug_packet(ec_dev->dev, "in", ptr, len + 3);
+
+	if (sum != ptr[len + 2]) {
+		dev_err(ec_dev->dev,
+			"bad packet checksum, expected %02x, got %02x\n",
+			sum, ptr[len + 2]);
+		return -EBADMSG;
+	}
+
+	return 0;
+}
+
+static int cros_ec_probe_spi(struct spi_device *spi)
+{
+	struct device *dev = &spi->dev;
+	struct cros_ec_device *ec_dev;
+	struct cros_ec_spi *ec_spi;
+	int err;
+
+	spi->bits_per_word = 8;
+	spi->mode = SPI_MODE_0;
+	err = spi_setup(spi);
+	if (err < 0)
+		return err;
+
+	ec_spi = devm_kzalloc(dev, sizeof(*ec_spi), GFP_KERNEL);
+	if (ec_spi == NULL)
+		return -ENOMEM;
+	ec_spi->spi = spi;
+	ec_dev = devm_kzalloc(dev, sizeof(*ec_dev), GFP_KERNEL);
+	if (!ec_dev)
+		return -ENOMEM;
+
+	spi_set_drvdata(spi, ec_dev);
+	ec_dev->name = "SPI";
+	ec_dev->dev = dev;
+	ec_dev->priv = ec_spi;
+	ec_dev->irq = spi->irq;
+	ec_dev->command_xfer = cros_ec_command_spi_xfer;
+	ec_dev->ec_name = ec_spi->spi->modalias;
+	ec_dev->phys_name = dev_name(&ec_spi->spi->dev);
+	ec_dev->parent = &ec_spi->spi->dev;
+	ec_dev->din_size = EC_MSG_BYTES + EC_MSG_PREAMBLE_COUNT;
+	ec_dev->dout_size = EC_MSG_BYTES;
+
+	err = cros_ec_register(ec_dev);
+	if (err) {
+		dev_err(dev, "cannot register EC\n");
+		return err;
+	}
+
+	return 0;
+}
+
+static int cros_ec_remove_spi(struct spi_device *spi)
+{
+	struct cros_ec_device *ec_dev;
+
+	ec_dev = spi_get_drvdata(spi);
+	cros_ec_remove(ec_dev);
+
+	return 0;
+}
+
+#ifdef CONFIG_PM_SLEEP
+static int cros_ec_spi_suspend(struct device *dev)
+{
+	struct cros_ec_device *ec_dev = dev_get_drvdata(dev);
+
+	return cros_ec_suspend(ec_dev);
+}
+
+static int cros_ec_spi_resume(struct device *dev)
+{
+	struct cros_ec_device *ec_dev = dev_get_drvdata(dev);
+
+	return cros_ec_resume(ec_dev);
+}
+#endif
+
+static SIMPLE_DEV_PM_OPS(cros_ec_spi_pm_ops, cros_ec_spi_suspend,
+			 cros_ec_spi_resume);
+
+static const struct spi_device_id cros_ec_spi_id[] = {
+	{ "cros-ec-spi", 0 },
+	{ }
+};
+MODULE_DEVICE_TABLE(spi, cros_ec_spi_id);
+
+static struct spi_driver cros_ec_driver_spi = {
+	.driver	= {
+		.name	= "cros-ec-spi",
+		.owner	= THIS_MODULE,
+		.pm	= &cros_ec_spi_pm_ops,
+	},
+	.probe		= cros_ec_probe_spi,
+	.remove		= cros_ec_remove_spi,
+	.id_table	= cros_ec_spi_id,
+};
+
+module_spi_driver(cros_ec_driver_spi);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("ChromeOS EC multi function device (SPI)");